This invention concerns an internal combustion engine cooling system and in particular means for filtering engine cooling air before it passes over a heat exchanger, such means being particularly useful on agricultural harvesting machines such as combines.
It has become conventional to at least partially enclose the engines of mobile harvesting machines and to mount a heat exchanger such as a radiator, for cooling the engine within the enclosure. It is also well-known to provide screens for filtering the cooling air drawn into the enclosure and also to provide means for removing from the screen accumulations of foreign materials such as chaff and leaves which occur in typical harvesting conditions.
Ideally, foreign material or trash removal should be automatic and continuous. Well-known attempts to achieve this include the use of rotating screens in conjunction with baffles or ducts adjacent the screen to upset the flow of cooling air through the screen so that foreign material has an opportunity to fall off or be drawn off. U.S. Pat. No. 3,837,149 West et al, also assigned to the assignee of the present invention, is an example of this general type of device. A fixed exhaust duct spans a portion of the exterior of a rotating screen so that air is drawn through the duct and locally reverses the flow of air through the screen so that foreign material accumulated on the screen is removed and carried through the duct. This type of self-cleaning filter arrangement is effective but does involve the complication of a drive to and sealing of the rotary screen. Typically, there is also the nuisance of the protuberance of the exhaust duct, beyond the periphery of the rotating screen.
U.S. Pat. No. 3,155,473 McNeil exemplifies another form of self-cleaning cooling air screen. Here the screen is stationary and a radially extending air duct rotates and sweeps the downstream or interior surface of the screen. The duct carries a propeller blade so that the flow of incoming air provides power to rotate the duct. An air passageway, with an inlet on the delivery side of the cooling fan, diverts some of the exhausting cooling air and feeds it to the "cleaning" duct so that, immediately in front of the duct, there is a reverse air flow, from the inside to the outside of the screen, tending to blow foreign material from the outside surface of the screen. This dislodged material is engaged by a sweeper vane which rotates with the duct to deflect the material away from the screen. This system obviously does not positively remove material away from the screen. Although the action of the sweeper vane may be to disperse some of the material radially outwards beyond the screen, there is the possibility of loss of control of the removed trash so that it may be again drawn onto the external surface of the screen. A further disadvantage of the McNeil system is the cost of providing the three separate components--propeller, duct, and sweeper vanes.